Apparatus for supplying heated air to blast furnaces and the like



July 4, 1950 J. F. MOWAT APPARATUS FOR SUPPLYING HEATED AIR T0 BLASTFURNACES AND THE LIKE 3 Sheets-Sheet 1 Filed Jan. 11, 1949 hwenlar:Joy/v f. Mon 4T,

fi/is War-neg July 4, 1950 .J. F. MOWAT 2,514,084

APPARATUS FOR SUPPLY HEATED AIR T0 BLAST FURNACES THE LIKE Filed Jan.11. 1949 3 Sheets-Sheet 2 hwentar: Jae N Man 0r,

@AMQKQW July 4, 1950 J. F. MOWAT 2,514,084

APPARATUS FOR SUPPLYING HEATE IR TO BLAST FURNACES AND THE L Filed Jan.11, 1949 3 Sheets-Sheet 3 hwem'far: JOH/V f Marwf,

Patented July 4, i950 APPARATUS FOR SUPPLYING HEATED AIR TO BLASTFURNACES AND THE LIKE John F. Mowat, La Grange, Ill., assignor toCarnegie-Illinois Steel Corporation, a. corporation of New JerseyApplication January 11, 1949, Serial No. 70,296

2 Claims.

This invention relates to an apparatus for supplying heated air tofurnaces and more particularly to improved apparatus for supplying hotblast to a. blast furnace through the use of recuperators.

While there have been many improvements made in the construction ofblast furnace stoves, the basic design has remained the same for manyyears. Stoves in use prior to my invention have been mainly of theregenerative type consisting generally of a cylindrical steel shelllined with fire brick which surrounds a brick checkerwork filledinterior. In operation, blast furnace gas is burned in a combustionchamber located near the bottom of the stove. The products of combustion arise from the combustion chamber and, following a plurality ofpasses through the brick checkerwork, pass out of the stove to a wastegas stack. After the checkerwork has been heated to a temperature ofapproximately 2000 F., the fuel gas inlet and the waste gas outlet areclosed, and air from blowers is admitted to the stove, Where in itstravel through the checkerwork it is heated to a temperature ofapproximately 1600 F., before entering the hot blast main.

Since the blast furnace operates most satisfactorily at a temperaturefixed by conditions existing within the furnace, generally in theneighborhood of between 900 and 1200 F., it is necessary to make use ofa so-called mixer valve through which air from a cold blast pipe,

at a temperature of about 150 to 175 F., is admitted to the hot blastmain in volume sufficient to cool the hot blast to the desiredtemperature before it actually enters the furnace.

As the cold blast continues to blow through the checkers, they graduallycool, thereby causing a drop in the temperature of the blast leavin thestove. During this time, the volume of cold blast being admitted throughthe mixer valve is reduced in order to keep the temperature of the blastentering the furnace constant. This requires continuous manipulation ofthe mixer valve which, as is well known to those versed in the art,results in intermitmnt operation and low thermal efliciency. The presentinvention proposes to solve this problem by maintaining the hot blast ata constant temperature through the use of recuperators whose operationis automatically regulated in the manner presently to be described.

It is, accordingly, an object of my invention to provide a system forsupplying heated air to blast furnaces using recuperators.

Another object of my invention is to provide a system for supplying thehot blast to a blast furnace using recuperators fired with gaseous,liquid or solid fuel in independent combustion chambers, the products ofcombustion being diluted with partiallycooled products of combustionthat have passed through the recuperators,

in controlled relationship, so that the temperature of the air leavingthe recuperators will be maintained substantially constant at anydesired temperature suited to conditions existing in the blast furnace.

These and other objects will become more apparent after referring to thefollowing specification and attached drawings, in which:

Figure 1 is a plan View of the system of my invention;

Figure 2 is an enlarged plan view of one recuperator and combustionchamber;

Figure 3 is a plan view, partly in section, of a recuperator andcombustion chamber;

Figure 4 'is a sectional view taken on the line IVIV of Figure 3; and

Figure 5 is a longitudinal sectional view showing amodification of thecombustion chamber of Figure 4.

Referring more particularly to the drawings, reference numeral 2indicates a recuperator having an independent refractory combustionchamber 4 connected thereto. Although the recuperator illustrated is ofthe tubular type it will be noted that any type may be used so long asthe mode of operation thereof involves passing of products of combustionthrough passages, the walls of which are exposed to the hot gases on oneside and to the air being heated on the other. Clean blast furnace gasis burned in the combustion chamber 4 through a burner 6 which issupplied from a fuel main 8 by means of a connecting duct I0. Although Ihave shown blast furnace gas as a preferred fuel, it is to be notedthat-liquid, solid or other gaseous fuels may be used equally as well. i

As best shown in Figure 4, the combustion chamber is constructed with acurved roof I 2 to impart a whirling motion to the products ofcombustion to promote a good mixture of the gases. In order to promotefurther turbulence and additional mixing of the gases before they enterthe recuperator through a header [6, cooled waste gases which havepreviously traversed the recuperator are recirculated into thecombustion chamber by means of pipes M which are installed at an angleas shown in Figures 1, 2 and 3. The pipes M are connected 3 to a wastegas main by means of a duct 20. If desired, baflles may be installed inthe header I 8 to promote additional mixing and distribution of thegases.

Although Figure 1 shows five recuperators in my system, it will be notedthat the number of recuperators necessary depends upon the requirementsof the blast furnace 34 and the size and type of recuperator used. Amultiplicity of recuperators of such size are used that one less thanthe total number will have suflicient capacity to heat all the airrequired by the blast furnace 34. In regular service all units will bein use but, when necessary, any one may be taken out of service withoutinterfering with the operation of the furnace.

The recuperators 2, as best shown in Figure 1, are arranged in parallelso that the cold blast which is delivered from the blast furnace blowersor blowing engines through a pipe 36 and individual connecting pipes 38can be distributed to each of the recuperators. The distribution is keptuniform by adjustment of the valves 40 which are provided'in each of thepipes 38. The air passing through the recuperators is heated to apredetermined temperature, as will be hereinafter more fully explained,and is delivered through valves 42, which are normally open, to the hotblast main 44, and thence to the blast furnace 34 through a bustle pipe46 and tuyeres 48.

The products of combustion from the burners 6 pass through and heat therecuperators 2 and pass therefrom to a waste gas flue 50 which connectsto a main line 52, from which the waste gases are removed by the naturaldraft of a stack 54. Chimney valves 56, which maybe used to regulate thedraft, are provided in the individual waste gas flues 50. Although Ihave shown the removal of the waste gases by means of the natural draftof stack 54, it may be noted that under certain conditions it may bedesirable to utilize induced draft in the flue for this purpose. Thismay be accomplished by providing an induced draft fan within flue 52.

A fan 60 is connected to the stack 54 by a pipe 58 and is driven by amotor or turbine 62. The

fan draws cooled products of combustion or waste gas from stack 54 anddelivers it to pipe l8 and ducts 28 fromwhich pipes l4 connect tocombustion chambers 4. To provide a mixture of the cooled products ofcombustion with the hot gases delivered by the burners 6, so that theresultant mixture will heat the recuperators to the temperature requiredto heat the blast to the proper temperature, it is necessary that thegases be properly proportioned. To accomplish this, the total heat inputto each recuperator is adjusted by automatically controlling the amountof fuel introduced into burner 6 in accordance with the temperature ofthe hot blast leaving the recuperator through valve 42 whilesimultaneously automatically controlling the amount of cooled waste gasflowing through duct 20 in accordance with the temperature of the gasmixture entering the recuperator from combustion chamber 4.

To control the amount of fuel flowing into each burner 6, I haveprovided a valve 64 in each connecting duct l0. Valve 64 isautomatically regulated in accordance with the temperature of the hotblast leaving the recuperator by means of a thermocouple 56, which isinserted into each recuperator immediately adjacent valve 42 andconnected to an indicating controller 68 which operates a relay 70which, in turn, actuates a motor drive 12 connected to valve 64.

The amount of cooled waste gas entering each combustion chamber 4 iscontrolled, in accordance with the temperature of the gas mixtureentering each recuperator, by means of a valve 14 provided in each duct20. Valve 14 is automatically regulated by a thermocouple 16 which isinserted in each recuperator and connected to an indicating controller18 which operates a relay which, in turn, actuates a motor drive 82connected to valve 14. Valve 14 is regulated in such a manner that whenthe temperature of the gas mixture entering th recuperator rises above apredetermined point, more cooled waste gas will be admitted, and whenthe temperature drops below this point, less cooled waste gas will beadmitted. Valves 84 are provided in pipes 14 to be used, when necessary,to, balance the flow of gas therethrough.

Figure 5 shows a modification 22 of the combustion chamber. Thismodified chamber is provided with a flat roof 24 and has a bridge wall26 in its interior arising vertically from its fioor. The burnerarrangement differs from that provided for combustion chamber 4 in thata burner 28, firing into chamber 22, projects through and is surroundedby a waste gaspipe 30. The fiame from the burner 28 is directed againstthe bridge wall 26 to provide better mixing of the hot gases with thecooled waste gas which is introduced through pipe 30; and also to avoiddirect impingement of the high temperature flame on the exposed surfacesof the recuperator 32. If desired, a multiplicity of burners may be usedas required to give the desired heat input with different types of fuel,and also with different sizes of recuperators.

Direct means for "backdrafting have been provided in my system byinstalling a pipe 86 .which connects the hot blast main 44 to the stack54. A shutoflf valve 88 is provided in the pipe 85. Another shutoffvalve 90 and an automatic relief valve 92 are provided in the hot blastmain 44. When it is desired to backdraft while changing tuyeres,blowpipes or coolers, valve 90 is closed and valve 88 is opened. At thesame time, the blowing engines or blowers ar slowed down, and the hotblast coming from the recuperators is delivered to the atmosphere by theautomatic relief valve 92. Thus the natural draft of the stack 54creates a backdraft through the pipe 86.

In the operation of the system of my invention the hot blast required bythe blast furnace under any existing condition is delivered from theblowers in the correct amount to each of the recuperators, where it isheated to the temperature desired and then delivered to the furnacecontinuously in regular unchanged volume and temperature, exactlyadapted to the needs of the blast furnace.

Should it be necessary to shut down a recuperator for any reason, burner6 of the recuperator is shut off, the chimney valve 56 is closed, as arevalves 40, 42 and 14. When this is done, the additional load istransferred to the other recuperators by increasing the heat inputthereto accordingly.

While one embodiment of my invention has been shown and described itwill be apparent that other adaptations and modifications may be madewithout departing from the scope of the following claims.

I claim:

1. In a system for supplying a heated blast to a furnace, a recuperator,a hot blast main for conducting the hot'blast from said recuperator tosaid furnace, a cold blast main for supplying air to be heated to saidrecuperator, a combustion chamber adjacent said recuperator, a burnerfiring into said combustion chamber, means for supplying fuel to saidburner, a passage for conducting cooled combustion gases from therecuperator to the atmosphere, a backdraft pipe extending from saidpassage to said hot blast main, a valve in said backdraft pipe for theclosing thereof while the hot blast is being conducted to the furnace, avalve in said hot blast main for the closing thereof while saidbackdraft pipe valve is open, and a relief exhaust valve in said hotblast main intermediate said hot blast main valve and said recuperator.

2. In a system for supplying a heated blast to a furnace, a plurality ofrecuperators, a hot blast main for conducting the hot blast from saidrecuperators to said furnace, a cold blast main for supplying air to beheated to said recuperators, a combustion chamber adjacent each of saidrecuperators, a burner firing into each of said combustion chambers,means for supplying fuel to said burners, a passage for conductingcooled combustion gases from the recuperators to the atmosphere, abackdraft pipe extending from said passage to said hot'blast main, avalve in said backdraft pipe for the closing thereof while the hot blastis being conducted to the furnace, a valve in said hot blast main forthe closing thereof while said backdraft pipe valve is open, and arelief exhaust valve in said hot blast main intermediate said hot blastmain valve and said plurality of recuperators.

JOHN F. MOWAT.

REFERENCES CITED The following references are of record in th

